An optical head and a disk recording/reproducing apparatus have been used in various applications such as DVD-RAM, DVD-ROM, MD, CD, and CD-R year after year, and have had even higher density, performance, quality, and added values. In recent years, the disk recording/reproducing apparatus particularly has advanced to higher density, which requires a further improvement in performance, quality, and function of the recording/reproducing system.
As the recording information of an optical disk medium becomes higher density, more improved accuracy and performance of the optical head are demanded strongly. In particular, the optical axis of an objective lens in the optical head should be precisely perpendicular to the optical disk medium. When a tilt error (also referred to as a tilt) occurs between the optical head and the optical disk medium, a technology to detect and correct the tilt error with high precision is required (see, e.g., JP 2001-167461 A).
There have been many reports on technologies for a tilt detector and a tilt corrector of the optical head in the disk recording/reproducing apparatus. An example of a conventional tilt detector of the optical head in the disk recording/reproducing apparatus will be described below by referring to the drawings.
FIG. 24 shows the schematic configuration and operating principle of a conventional tilt detector of an optical head (see, e.g., JP 60(1985)-127630 U).
In FIG. 24, reference numeral 80 is an optical disk, 81 is an optical head, 82 is a light-receiving element, 83 is a differential amplifier, 84 is a LED (light source), and 85a and 85b are photodetectors. Moreover, reference numeral 2 is a semiconductor laser, 79 is an objective lens, 47 is a turntable, 86 is a carrier, 87 is a driving gear, 88 is a DC motor, and 89 is a tilt fulcrum.
The turntable 47 holds the optical disk 80 on the holding surface and rotates it precisely at a predetermined number of revolutions around a rotation central axis R.
The optical head 81 includes the semiconductor laser 2, the objective lens 79, and an objective lens drive (not shown). Alight beam from the semiconductor laser 2 enters the objective lens 79. The objective lens drive moves the position of the objective lens 79 relative to the optical disk 80 in focusing and tracking (radial) directions so that the position of a light spot formed on the optical disk 80 is controlled accurately. Moreover, light is focused on a predetermined information track of the optical disk 80, and the reflected light from the optical disk 80 is detected by the light-receiving element 82, thereby reproducing the information of the optical disk 80.
The optical disk 80 is irradiated with light from the LED 84, and the reflected light is received by the photodetectors 85a, 85b that are provided in the optical head 81. Then, the differential amplifier 83 calculates a difference between the outputs of the photodetectors 85a and 85b. In this tilt detector, light from the LED 84 is reflected by the optical disk 80 and reaches the photodetectors 85a, 85b. 
When a tilt of the optical disk 80 with respect to a predetermined reference value is 0° (small) or when the relative inclination between the optical disk 80 and the optical head 81 is 0° (small), that is, when the optical axis of the objective lens 79 is perpendicular to the optical disk 80, the amount of reflected light reaching the photodetector 85a is substantially the same as that reaching the photodetector 85b. 
When the optical disk 80 tilts, the reflected light from the optical disk 80 is displaced toward either of the photodetectors 85a, 85b. Therefore, an electrical signal corresponding to the tilt direction of the optical disk 80 can be obtained as an output of the differential amplifier 83 that calculates a difference between outputs of the photodetectors 85a and 85b. 
For tilt correction, the optical head 81 is moved around the tilt fulcrum 89 in the radial direction of the optical disk 80 with respect to the carrier 86 by the driving gear 87, the DC motor 88, or the like, so that the optical head 81 is moved in the V direction of FIG. 24. In this case, the tilt between the optical disk 80 and the optical head 81 can be corrected in such a manner that a voltage corresponding to the output of the differential amplifier 83 is applied to the DC motor 88, and then the whole optical head 81 is inclined with respect to the carrier 86 or the optical disk 80 by using the driving gear 87 or the like.
In the conventional tilt detector of the optical head, however, variations in the angle of divergence or the emission point of the LED 84 are increased excessively, which leads to a larger variation in the amount of light received by the photodetectors 85a, 85b. Therefore, not only the detection sensitivity that is the ratio of a change in output of the differential amplifier 83 to the amount of radial tilt of the optical disk 80, but also the tilt detection accuracy of the optical disk 80 is varied significantly.
Moreover, the relative position between the LED 84 and the photodetectors 85a, 85b is changed greatly, which requires accurate positioning of the emission point of the LED 84 and the photodetectors 85a, 85b. Therefore, the number of positioning steps is increased, and the positions of the LED 84 and the photodetectors 85a, 85b also are varied significantly. This causes a variation in outer shape accuracy of the optical head 81.
Further, the LED 84 that serves as a light source is provided separately on the optical head 81. Thus, it is difficult to reduce the size and thickness of the optical head 81, and the assembly steps and the component cost are raised considerably.
The conventional tilt corrector is configured so that the whole optical head 81 is inclined with respect to the carrier 86. Therefore, the optical head 81 including the tilt corrector becomes larger in size, and thus it is difficult to reduce the size of the disk recording/reproducing apparatus. In addition, the responsiveness of tilt correction is degraded.
Thus, the tilt correction of the optical head 81 requires a waiting time for the system, so that a tilt cannot be detected in real time at high speed during recording or reproduction. Consequently, it is not possible to achieve tilt correction with excellent responsiveness.